1. Field of the Invention
The present invention relates to an ink jet head for recording on various recording media, such as paper, yarns, fibers, textile, leather, metal, plastics, glass, timber and ceramics. The term “recording” above means providing a recording medium with not only a meaningful image such as a character or a graphic image, but also a meaningless image such as a pattern.
2. Description of the Related Art
As an ordinary ink jet head, there will be described an ink jet head in which the ink discharge is executed perpendicularly to the plane of an energy generating element for generating energy to be utilized for ink discharge. In recent years, in order to meet the requirement for compactification and higher density, an ink jet head is proposed in a structure of incorporating an electric control circuit, for driving the energy generating element, in a substrate utilizing the semiconductor manufacturing technology. In the aforementioned ink jet head of high performance, the compactification and the high image quality are accomplished by forming a common ink supply opening penetrating through the substrate from the rear surface thereof, and arranging a plurality of nozzles (discharge ports and flow paths communicating thereto) on both sides of the opening in the substrate. Such ink jet head of high performance is already commercialized up to a nozzle array density of 600 dpi, on one side of the opening.
However, a further increase in the nozzle array density requires a high investment in the manufacturing apparatus for forming a high-definition pattern. Therefore proposed is a structure of maintaining the nozzle array density at 600 dpi but displacing the nozzle positions (positions of discharge ports) on both sides of the common ink supply opening by half a pitch, with respect to each other. In this manner, the practical nozzle density at recording is doubled to 1200 dpi, thereby achieving a higher image quality in the recorded image. Such structure is disclosed in U.S. Pat. No. 6,830,317.
Also U.S. Pat. No. 6,390,606 discloses a process of forming a flow path, by forming a mold pattern for the flow path, then covering it with a resin constituting a flow path forming member, and then removing the mold. Also this patent discloses, in relation to the adhesivity between the substrate and the nozzle layer, to provide a polyether amide resin as an adhesion layer between the substrate and the nozzle layer.
However, in order to attain an even higher image quality in the image recorded by the recording head, further technical developments are necessary for realizing a higher density in the nozzle array while minimizing the investment.
The aforementioned process disclosed in U.S. Pat. No. 6,390,606 has a certain limitation in the patterning precision of the mold material for the flow path pattern in case of the conventionally utilized materials, but is capable of forming satisfactory flow path wall 106 as illustrated in FIGS. 6A, 6B, 6C, 6D, 6E, 6F, 6G and 6H, up to the conventional nozzle density (600 dpi). In this case, the flow path wall 106 has an aspect ratio (ratio of height and width) of 4:3. However, when the nozzle density is increased to 1200 dpi, the mold material, formed by a photosensitive material, shows a deficiency in resolution, whereby the flow path wall 106 cannot be satisfactorily formed. For example, when a gap is formed between the end portion of the flow path wall 106 and the adhesion layer 107 as illustrated in FIG. 8, the adjacent flow paths are mutually connected to generate a crosstalk, whereby the ink cannot be discharged in a satisfactory manner.
In order to solve such limitation, it is conceivable to change the mold material to a material of a higher resolution. However, such material of a higher resolution is difficult to develop within a short period. As another method, it is conceivable to reduce the thickness of the mold material. However, in the case that the nozzle density is increased to 1200 dpi, the width of each flow path becomes smaller, thus being liable to cause a deficient ink refill to the discharge port. Therefore, in order to secure the cross section of each flow path and to prevent such deficient refill, it is necessary to increase the height of each flow path. Therefore, it is impractical to reduce the thickness of the mold material. Therefore, the two methods mentioned above are incapable of solving the problems which result when the nozzle density is increased.